Meteor collection sort by $size issue

Question

This is about likes and dislikes on comments. I'd like to sort comments by likeness, so a comment with more likes will appear first. The issue is that comments with dislikes appear before than comments with no dislikes.

What i want:

Comment A : 1 like 0 dislikes
Comment B : 0 like 0 dislike
Comment C : 0 like 1 dislike

What I'm actually getting:

Comment A : 1 like 0 dislikes
Comment C : 0 like 1 dislike
Comment B : 0 like 0 dislike

My mongo query on my meteor helper:

Missatges.find({ topic: 'xxx' }, { sort: { like:{ $size: -1}, dislike:{ $size: 1}, date: -1 } }).fetch();

Note that I use $size because like and dislike are arrays of user _id's. Here my comment schema:

author: {
    type: String

},
authorId: {
    type: SimpleSchema.RegEx.Id
}
isAnswer: {
    type: Boolean
},
parentId: {
    type: SimpleSchema.RegEx.Id,
    optional: true
},
date: {
    type: Date
},
topic: {
    type: String
},
likes: {
    type: [SimpleSchema.RegEx.Id]
},
dislikes: {
    type: [SimpleSchema.RegEx.Id]
},
answers: {
    type: [SimpleSchema.RegEx.Id],
    optional: true
},
text: {
    type: String,
    max: 900,        
}

What ever result it is returning is the way the query, that you are using, should return. — Shrabanee, Jun 03 '16 at 11:27
Maybe it's my english, perhaps it's yours... but sorry, I don't understand your comment @titi23 — Vice Sallés, Jun 03 '16 at 11:40
The result you are getting by running the query, is right. That is how the query suppose to return. Hope it is clear now. — Shrabanee, Jun 03 '16 at 11:41

score 1 · Accepted Answer · answered Jun 03 '16 at 12:27

According to the answer to this question you can't use $size to sort in mongo. One solution is to fetch the matching documents and sort them in the helper. Here's an example (note this is untested and may require some tweaking):

Template.something.helpers({
  sortedThings: function () {
    return Missatges
      .find({ topic: 'xxx' })
      .fetch()
      .sort(function (b, a) {
        var al = a.likes.length;
        var ad = a.dislikes.length;
        var bl = a.likes.length;
        var bd = a.dislikes.length;
        var d1 = a.date;
        var d2 = b.date;

        // compare by likes
        if (al > bl) return 1;
        if (al < bl) return -1;

        // compare by dislikes
        if (ad < bd) return 1;
        if (ad > bd) return -1;

        // compare by date
        if (d1 > d2) return 1;
        if (d1 < d2) return -1;

        // they are equal
        return 0;
      });
  },
});

It should be possible to have the custom sort function passed in the `sort` attribute of the second argument to `find()` itself once [this issue](https://github.com/meteor/meteor/issues/2730) is fully resolved (I intend to submit a PR soon). — MasterAM, Jun 03 '16 at 12:32
Thank you David, finally, though, I opted for the solution presented on the link you provided me. I added 2 Number fields to the model: nLike and nUnlikes. It gets more handy even in other use cases I have — Vice Sallés, Jun 06 '16 at 06:04

Meteor collection sort by $size issue

1 Answers1